Endothelial cells (ECs) play a major role in maintaining normal hemostasis and vascular patency by regulating the balance between synthesis of coagulant proteins that promote fibrin and clot formation and fibrinolytic proteins that facilitate clot lysis. The overall goal of these studies is to establish whether the not expression of EC surface-localized fibrinolytic activity (plasmin generation) may be defective (decreased) in different human cultured EC types (umbilical vein, placental microvessel, aorta, coronary artery) derived from blacks vs. whites (and gender groups). This will result in a shift in the hemostatic balance on the EC surface towards thrombogenicity which may contribute, in part, to the pathogenic mechanism(s) underlying the Increased incidence of coronary artery disease (CAD) In black Americans. Specifically, we will determine and compare: EC fibrinolytic protein (u-PA, t-PA and PAI-1) activity, antigen and mRNA levels in different cultured human EC types (fibrin autography, PAs/PAI-1 activity assays, ELISAs, Northern blot analysis, reverse transcriptase PCR [RT-PCR] and in situ hybridization) (Aim 1); levels of EC receptor (R) proteins involved In the regulation, surface-localization and net expression of EC surface-localized fibrinolysis (ligand binding/Scatchard analysis, fluorogenic substrate/1251-labeled-Lys-Pmg activation) (Aim 2); effects of select modulators (rIL-l, rTNFalpha and thrombin) on maximal response and expression of PAs/PAI-1 /u-PAR antigen and mRNA levels (ELISAs, ligand binding/Scatchard analysis, Northern blot analysis) (Aim 3). Finally, we will determine and compare the presence/formation and fibrinolytic activity/potential of multinucleated giant cell phenotypes in cultured EC types derived from different racial/gender groups (Aim 4). These comparative studies will establish whether defective EC fibrinolysis may have a pathogenic role in the differential expression of CAD in racial groups.